I. Technical Field
This invention pertains to wireless telecommunications, and particularly to operation of a femto radio base station in a radio access network (RAN)
II. Related Art and Other Considerations
In a typical cellular radio system, wireless user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. Alternatively, the wireless user equipment units can be fixed wireless devices, e.g., fixed cellular devices/terminals which are part of a wireless local loop or the like.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks. The core network has two service domains, with an RNC having an interface to both of these domains.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies.
As those skilled in the art appreciate, in WCDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handover of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
Other types of telecommunications systems which encompass radio access networks include the following: Global System for Mobile communications (GSM); Advance Mobile Phone Service (AMPS) system; the Narrowband AMPS system (NAMPS); the Total Access Communications System (TACS); the Personal Digital Cellular (PDC) system; the United States Digital Cellular (USDC) system; and the code division multiple access (CDMA) system described in EIA/TIA IS-95.
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface” or “Uu interface”. In some instances, a connection involves both a Source and Serving RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handled by the DRNC. An Inter-RNC transport link can be utilized for the transport of control and data signals between Source RNC and a Drift or Target RNC, and can be either a direct link or a logical link. An interface between radio network controllers (e.g., between a Serving RNC [SRNC] and a Drift RNC [DRNC]) is termed the “Iur” interface.
The radio network controller (RNC) controls the UTRAN. In fulfilling its control role, the RNC manages resources of the UTRAN. Such resources managed by the RNC include (among others) the downlink (DL) power transmitted by the base stations; the uplink (UL) interference perceived by the base stations; and the hardware situated at the base stations.
Those skilled in the art appreciate that, with respect to a certain RAN-UE connection, an RNC can either have the role of a serving RNC (SRNC) or the role of a drift RNC (DRNC). If an RNC is a serving RNC (SRNC), the RNC is in charge of the connection with the user equipment unit (UE), e.g., it has full control of the connection within the radio access network (RAN). A serving RNC (SRNC) is connected to the core network. On the other hand, if an RNC is a drift RNC (DRNC), it supports the serving RNC (SRNC) by supplying radio resources (within the cells controlled by the drift RNC (DRNC)) needed for a connection with the user equipment unit (UE). A system which includes the drift radio network controller (DRNC) and the base stations controlled over the Iub Interface by the drift radio network controller (DRNC) is herein referenced as a DRNC subsystem or DRNS. An RNC is said to be the Controlling RNC (CRNC) for the base stations connected to it by an Iub interface. This CRNC role is not UE specific. The CRNC is, among other things, responsible for handling radio resource management for the cells in the base stations connected to it by the Iub interface.
Some operators are investigating the possibility of providing home or small area WCDMA coverage for limited number of users using a small radio base station (“RBS”), also called a “Femto RBS” and/or a “Home RBS” and/or “pico RBS” and/or “micro RBS” in some contexts. According to such investigation, the small RBS would provide normal WCDMA coverage for the end users (e.g., to a user equipment unit (UE)), and would be connected to the RNC using some kind of IP based transmission. The coverage area so provided is called a “femto cell” (to indicate that the coverage area is relatively small). Other terminology for a femto cell includes “pico cell” or “micro cell”, which is in contrast to a macro cell covered by a macro or standard radio base station (RBS).
One alternative for the IP based transmission is to use Fixed Broadband access (like xDSL, Cable etc.) to connect the home RBS to the RNC. Another alternative would be to use Mobile Broadband access (e.g. HSDPA and Enhanced Uplink). FIG. 12 illustrates the two different backhaul alternatives in more detail. The first alternative is labeled “xDSL Backhaul” and the second alternative is labeled “WiMAX Backhaul”.
In general, ordinary WCDMA base stations (macro RBS) are able to connect to an RNC using IP-based transmission. Operator personnel, e.g., employees of an operator company which owns or maintains the macro RBS nodes and RNC nodes of the radio access network (RAN), typically install the macro RBS nodes. As part of the installation, the macro RBS is manually configured with IP addressing information (DNS name, Fully Qualified Domain Name, FQDN, or IP-address) of the RNC to which the macro RNC is to connect.
By contrast, a femto RBS is typically installed by the end user rather than the network operator. The end users are also able to move the Femto RBS geographically from place to place without the operator being able or willing to control relocation of the femto RBS. Such user-directed relocation requires that, wherever the Femto RBS is installed or located, it should connect to the correct RNC. A “correct RNC” or “preferred RNC” in this sense would be the same RNC that is controlling the overlaying macro cell of the radio access network (RAN), e.g., a “correct macro RNC” or “preferred macro RNC”.
Connection to the correct RNC is important since, e.g., it also improves the building of the neighboring cell lists that are needed for roaming and handover between the femto RBS and macro RBS cells. In addition it also minimizes network signaling between control nodes.
Thus, the current technique of manually configuring the RBS with the RNC IP addressing information does not work for the femto RBS scenario, since, e.g., the femto RBS is to be installed by the end users.
What is needed, therefore, and an object herein provided, are method, technique, apparatus, and systems for selecting a correct RNC to serve an femto RBS, for example an IP-connected femto RBS. Such object is particularly valuable when the femto radio base station does not have its own capability to discern the radio access network environment, e.g., when the femto radio base station does not have its own receiver or user equipment unit, for example.